Apple has released a developer preview of OS X Mountain Lion, the ninth major release of the operating system. According to Apple, it brings popular apps and features from the iPad to the Mac and accelerates the pace of OS X innovation.

Mountain Lion introduces Messages, Notes, Reminders and Game Center to the Mac, as well as Notification Center, Share Sheets, Twitter integration and AirPlay Mirroring. Mountain Lion is the first OS X release built with iCloud in mind for easy setup and integration with apps.

The developer preview of Mountain Lion also introduces Gatekeeper, a security feature designed to help keep you safe from malicious software by giving you complete control over what apps are installed on your Mac. The preview release of Mountain Lion is available to Mac Developer Program members starting today. Mac users will be able to upgrade to Mountain Lion from the Mac App Store in late summer 2012.

"The Mac is on a roll, growing faster than the PC for 23 straight quarters, and with Mountain Lion things get even better," says Philip Schiller, Apple’s senior vice president of Worldwide Marketing. "The developer preview of Mountain Lion comes just seven months after the incredibly successful release of Lion and sets a rapid pace of development for the world’s most advanced personal computer operating system."

The developer preview of Mountain Lion features the all new Messages app, which replaces iChat and allows you to send unlimited messages, high-quality photos and videos directly from your Mac to another Mac or iOS device. Messages will continue to support AIM, Jabber, Yahoo! Messenger and Google Talk.

Starting today Lion users can download a beta of Messages from http://www.apple.com, and the final version will be available with Mountain Lion. Reminders and Notes help you create and track your to-dos across all your devices. Game Center lets you personalize your Mac gaming experience, find new games and challenge friends to play live multiplayer games, whether they’re on a Mac, iPhone, iPad or iPod touch.

Mountain Lion presents notifications in an elegant new way, and Notification Center provides easy access to alerts from Mail, Calendar, Messages, Reminders, system updates and third party apps, according to Schiller. Systemwide Share Sheets make it easy to share links, photos and videos directly from Apple and third party apps, he adds.

Twitter is integrated throughout Mountain Lion so you can sign on once and tweet directly from Safari, Quick Look, Photo Booth, Preview and third party apps. Mountain Lion also introduces AirPlay Mirroring, a way to wirelessly send a secure 720p video stream of what's on your Mac to an HDTV using Apple TV.

More than 100 million users have iCloud accounts, and Mountain Lion makes it easier than ever to set up iCloud and access documents across your devices, says Schiller. Mountain Lion uses your Apple ID to automatically set up Contacts, Mail, Calendar, Messages, FaceTime and Find My Mac. The new iCloud Documents pushes any changes to all your devices so documents are always up to date, and a new API [application programming interface] helps developers make document-based apps work with iCloud.

Gatekeeper is a new security feature that gives you control over which apps can be downloaded and installed on your Mac. You can choose to install apps from any source, just as you do on a Mac today, or you can use the safer default setting to install apps from the Mac App Store, along with apps from developers that have a unique Developer ID from Apple. You can also set Gatekeeper to only allow apps from the Mac App Store to be downloaded and installed.

Mountain Lion also has features specifically designed to support Chinese users, including enhancements to the Chinese input method and the option to select Baidu search in Safari. Mountain Lion is designed to make it easy to set up Contacts, Mail and Calendar with top email service providers QQ, 126 and 163. Chinese users can also upload video via Share Sheets directly to leading video websites Youku and Tudou, and systemwide support for Sina weibo makes microblogging easy.

New APIs give developers access to new core technologies and enhanced features within OS X. The Game Kit APIs tap into the same services as Game Center on iOS, making it possible to create multiplayer games that work across Mac, iPhone, iPad and iPod touch. A new graphics infrastructure underpins OpenGL and OpenCL and implements GLKit, first introduced in iOS 5, to make it easier to create OpenGL apps.

According to Apple, using Core Animation in Cocoa apps is easier than ever, and new video APIs deliver modern 64-bit replacements for low-level QuickTime APIs. Enhanced Multi-Touch APIs give developers double-tap zoom support and access to the systemwide lookup gesture. Kernel ASLR improves security through enhanced mitigation against buffer overflow attacks.